The Flow of Electrons as Electric Current

Q.

Define electricity

Q. 93.A capacitor of 10 microfarad is charged to a potential 50V with a battery . The battery is now disconnected and an additional charge 200 microcoulomb is given to the positive plate of the capacitor . New potential difference across the capacitor will be

Q. In the Bohr’s model of hydrogen atom, the electrons moves around the nucleus in a circular orbit of a radius $5\times {10}^{-11}$ metre. It’s time period is $1.5\times {10}^{-16}$ sec. The current associated is

1. Zero
2. $1.6\times {10}^{-19}A$
3. $0.17A$
4. $1.07\times {10}^{-3}A$

Q.

The potential difference applied to an X-ray tube is 5 kV and the current through it is 3.2 mA. Then the number of electrons striking the target per second is

1. $2\times {10}^{16}$
2. $5\times {10}^6$
3. $1\times {10}^{17}$
4. $4\times {10}^{15}$

Q. The current through a wire depends on time as $I=(2+3t)\text{A}$. Calculate the charge crossed through a cross-section of the wire in $10\text{s}$.

1. $170\text{C}$
2. $17\text{C}$
3. $150\text{C}$
4. $20\text{C}$

Q.

A steady current flows in a metallic conductor of non uniform cross section .Explain which of these quantities is constant along the conductor and why? :current, current density, electric field and drift speed?

Q.

What is Coulomb in physics?

Q.

As shown in the figure, a battery of emf $ϵ$ is connected to an inductor $L$ and resistance $R$ in series. The switch is closed at $t=0$. The total charge that flows from the battery, between $t=0$ and $t=t_c(t_c\text{is the time constant of the circuit) is}$

1. $\frac{ϵL}{R^{2}e}$
2. $\frac{ϵL}{R^2}(1-\frac{1}{e})$
3. $\frac{ϵL}{R^2}$
4. $\frac{ϵR}{e{L}^2}$

Q. A capacitor is charged with a battery and energy stored is $U$. After disconnecting the battery, another identical uncharged capacitor is connected in parallel with it. The energy stored in each capacitor is now

1. $\frac{U}{2}$
2. $\frac{U}{4}$
3. $4U$
4. $2U$

Q.

What is the SI unit of surface charge density?

Q.

What Is The Basic Three Electrical Quantities?

Q. A beam of electrons moving at a speed of ${10}^6$ m/s along a line produces a current of $1.6\times {10}^{-6}A$. The number of electrons in the 1 metre of the beam is

1. ${10}^6$
2. ${10}^7$
3. ${10}^{13}$
4. ${10}^{19}$

Q. The radius of an orbit of electron in hydrogen atom is $5\times {10}^{-11}m$. If the speed of electron is $2.2\times {10}^8$ m/s then the equivalent current due to orbital motion of electron is

1. 3.14 A
2. 11.2 A
3. 0.01 A
4. 0.112 A

Q. A parallel plate capacitor is charged by a battery to a potential difference $V$. It is disconnected from battery and then connected to another uncharged capacitor of the same capacitance. Calculate the ratio of the energy stored in the combination to the initial energy on the single capacitor.

Q. In an intrinsic semiconductor, the number of conduction electrons is $9\times {10}^{19}$ per cubic meter. Find the total number of current carriers $\left(\text{electrons and hole}\right)$ in a semiconductor of size $1\text{cm}\times 1\text{cm}\times 1\text{mm}$

1. $9\times {10}^{12}$
2. $18\times {10}^{12}$
3. $9\times {10}^7$
4. $8\times {10}^7$

Q.

The current through a wire depends on time as i = $i_0+\alpha t,$ where $i_0$ = 10 A and $\alpha =4A{s}^{-1}$. Find the charge crossed through a section of the wire in 10 seconds.

Q. A combination of capacitors is set up as shown in the figure. The magnitude of the electric field, due to a point charge $Q$ (having a charge equal to the sum of the charges on the $4\mu F$ and $9\mu F$ capacitors), at a point distant $30m$ from it, would equal

1. $240N/C$
2. $360N/C$
3. $420N/C$
4. $480N/C$

Q. Seawater at a frequency $f=9\times {10}^2\text{Hz}$ has permittivity $ϵ=80{ϵ}_o$ and resistivity $\rho =0.25\Omega \text{m}$. Imagine a parallel plate capacitor is immersed in seawater and is driven by an alternating voltage source $V\left(t\right)=V_o\sin \left(2\pi ft\right)$. Then, the conduction current density becomes ${10}^x$ times the displacement current density after time $t=\frac{1}{800}\text{s}$. The value of $x$ is ______.

$(\frac{1}{4\pi {ϵ}_o}=9\times {10}^9{\text{Nm}}^2{\text{/C}}^2)$

Q. The belt of an electrostatic generator is $50cm$ wide and travels $30cm/s$. The belt carries charge into the sphere at a rate corresponding to ${10}^{-4}A$. What is the surface density of charge on the belt?

1. $6.7\times {10}^{-7}C{m}^{-2}$
2. $6.7\times {10}^{-5}C{m}^{-2}$
3. $6.7\times {10}^{-4}C{m}^{-2}$
4. $6.7\times {10}^{-8}C{m}^{-2}$

Q. Electric bulb 50W-100V glowing at full pois used in parallel with battery 120V , 10ohm. Maximum number of bulbs that can be connected so that they glow in full power is ??

Q.

In an electrolyte $3.2\times {10}^{18}$ bivalent positive ions drift to the right per second while $3.6\times {10}^{18}$ monovalent negative ions drift to the left per second. Then the current is

1. 1.6 amp to the right
2. 1.6 amp to the left
3. 0.45 amp to the right
4. 0.45 amp to the left

Q.

a wire of resistance 18 ohm is bent to form an equilateral triangle. The resistance across any two vertices of the triangle is(in ohm)

Q.

Three identical bulbs P, Q and R are connected to a battery as shown in figure. When the circuit is closed

1. Q and R will be brighter than P

2. All the bulbs will be equally bright

3. Q and R will be dimmer than P

4. Q and R will not shine at all

Q. A current $I$ flows along a thin walled tube of radius $R$ with a long longitudinal slit of width $b(<<R)$. What is the value of magnetic field at the centre.

1. $\frac{{\mu }_{0}Ib}{4{\pi }^2{R}^2}$
2. $\frac{{\mu }_{0}Ib}{2{\pi }^2{R}^2}$
3. Zero
4. $\frac{{\mu }_{0}I}{4{\pi }^2{R}^2}$

Q. To keep the electric current flowing in a conductor continuously we need to maintain a constant difference across its terminals.

1. Temperature
2. charge density
3. pressure
4. electric potential

Q.

For a real battery the work done by battery is equal to increase in electrical potential energy of a positive charge as charge moves from negative terminal to positive terminal of battery

Is this above statement true. ??

Q. A source of emf $E=10\text{V}$ and having negligible internal resistance is connected to a variable resistance. The resistance varies as shown in figure. The total charge that has passed through the resistor $R$ during the time interval from $t_1$ to $t_2$ is

1. $40{\log }_{e}4$
2. $30{\log }_{e}3$
3. $20{\log }_{e}2$
4. $10{\log }_{e}2$

Q.

A current flowing through a wire depends on time as$I=3t^2+2t+5$. The charge flowing through the cross-section of the wire in time from $t=0$ to $t=2s$ is:

1. $22C$

2. $20C$

3. $18C$

4. $5C$

Q. A 500watt lamp gives light for 10 hours on electric mains if the cost of energy is 40 paise per unit find the cost of electric consumption

Q. The currect through a wire depends on time as,
$i=(10+4t)$
Here, $i$ is in ampere and $t$ in seconds. Find the charge crossed through a section in time interval between $t=0$ to $t=10\text{s}$.

1. $300\text{C}$
2. $400\text{C}$
3. $500\text{C}$
4. $600\text{C}$